From trees to humans, from elephants to the smallest bacteria, all living things today have a common ancestor, a tiny cell that the scientific community has dubbed LUCA. last universal common ancestor (“Last Universal Common Ancestor”).
But LUCA is not the origin of life. It is the oldest organism we can trace back to by analyzing the genes of living species. It is a formidable challenge for phylogeneticists, the genealogists of life. An international team proposes a reconstruction of LUCA’s genome and new dating work. Published in July in the scientific journal Nature and Evolution Environment.
“According to our estimates, this LUCA is a fairly complex object.”Its genome would contain plans for 2,600 proteins, a higher number than previously estimated, says Edmund Moody, an evolutionary biologist in the Palaeobiology Group at the University of Bristol in the United Kingdom and the study’s first author.
common core
To arrive at this number, the researchers first created a database of the genomes of prokaryotes, single-celled organisms found in the world today, such as bacteria. Then they used a new algorithm. “It allows, for each gene family, to determine the probability of being present in the LUCA genome.”“It is a very important finding,” explains Tom Williams, co-author and professor at the University of Bristol.
If we had an idea of the breed [la généalogie] Species, this method makes it possible to reconstruct the evolutionary scenario for each gene.specifies Vincent Dupin, CNRS research director at the Laboratory of Biometrics and Evolutionary Biology, in Villeurbanne (Rhône), who worked on the method but was not involved in the study.
Imagine a tree. Luca in The base of its trunk. All current species form leaves. The researchers reconstruct a tree for each gene to understand its history. They infer which genes from current prokaryotes were already present in LUCA.
Genes are passed on to descendants, from roots to leaves. But they can also be passed on between species, horizontally, between the branches of a tree. “This new method makes it possible to detect horizontal transport.”, The world continues to evolve.
“Doubts”
“These horizontal transfers are still difficult to see, especially when they are old. The danger is in overestimating the amount of genes present in LUCA.a nuance Purificación López García, research director at the Laboratory of Ecology, Systematics and Evolution at the University of Paris-Saclay. The biologist points out that “big doubts” From the study.
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